Manufacture of lead borate



Patented lien. 4, 1938 2.104549 MANUFACTURE OF LEAD BORATE Stephen W. Stockdale, Hammond, Ind., and Elbert F. Weaver and Samuel Paul Tinnes, Calumet City, 111., assignors to Anaconda Lead Products Company, a corporation of Delaware No Drawing.

Application August 1, 1936,

y Serial No. 93,816

9 Claims. (01. 204-9) This invention relates to the production of lead borate and has for an object the provision of an improved process for producing lead borate electrolytically. The invention further contem- 5 plates the production of an improved lead borate product.

The process of the invention is of the type employing a bifluid cell through which an electric current is passed from a lead anode immersed ill in an anolyte capable upon electrolysis of yield ing a lead solvent to an inert or insoluble cathode immersed in a suitable catholyte and separated from the anglyte by means of a suitable permeable diaphramn. I It has been proposed It heretofore to employ, processes of this type for the production of lead borate, but such processes as have been proposed have been lnefllcient because of improper or inefiective control of various factors afiecting the important physical w properties of the products or because of the use of improper anolyte and catholyte reagents, and the products of such processes have been of inierior duality and unsuitablefor many of the commercial applications of lead borate.

movements in the control of factors influencing the important physical properties of lead borate produced in bifiuid electrolytic cells and affecting emcient operation of cells so employed. The

3% invention also provides for the use of effective reagents in the preparation of anolytes and catholytes for bifiuidelectroiytic cells employed in the production of lead borate. Lead borate produced in accordance with the method of the invention is admirably suited for use in the ceramic industry.

In carrying out the process of the invention,

a lead anode is immersed in an anolyte containing a substance capable oi serving upon electrol- 4,o ysis as a solvent for lead. The invention particularly contemplates the use of anaqueous solutlon of a substance capable of yielding chlorate ions, such, for example, as sodium chlorate, as

the anolyte. A substance capable of yielding an borate ions such, for example, as sodium tetraborate (Nam-101) is employed as the catholyte.

(The word borate as used in this specification and the appended claims, unless qualified, refers generally to anions consisting of boron and oxyso gen in any of the well known proportions.) The process may be carried out in electrolyticeells of conventional design equipped with diaphragms oi the types usually employed in producing lead salts electrolytically. The apparatus preferably 5 includes means for withdrawing and circulating The present invention provides certain imboth the anolyte and the catholyte; circulation oi the anolyte and the catholyte preferably is carried out continuously during the course of the process, the lead borate produced being separated from the anolyte in any suitable manner after withdrawal of the anolyte from the cell and prior to its re-introduction into the cell. In the preferred process of the invention, the borate con tent of the catholyte is maintained at the desired value by the addition or boric acid (l-laBOs) thereto at a point outside the cell.

The various control features of the invention will be described hereinafter more particularly with reference to their application to a process employing an anolyte consisting essentially of a solution of sodium chlorate and a oatholyte consisting essentially of a solution of sodium tetraborate (Na2B407)- Incarrying out the process of the invention in its preferred and complete form, a lead anode is suspended in the anolyte compartment of a bifluid electrolytic cell in contact with an anolyte containing a substance capable of yielding chlo rate ions, e. g., sodium chlorate. A suitable inert or insoluble cathode is suspended in the catholyte compartment of the cell in contact with a catholyte containing sodium tetraborate. The cathode may be composed of any electricallyconducting material which is not adversely aiiected by the reagents with which it comes in contact'and which will not contaminate the product or the cell; iron is a particularly suitable substance ior this purpose.

The anolyte and catholyte compartments of the cell are separated by a suitable permeable diaphragm. which serves to prevent actual raising of the anolyte and'catholytesolutions, but which permits the passage of current from the anolyte to the catholyte and diffusion of ions in solution in the catholyte into the anolyte. The diaphragm also serves to prevent passage into the anolyte of insoluble lead borate produced in the anolyte during electrolysis;

As pointed out above, means are provided for circulating anolyte and catholyte through the anolyte and catholyte compartments, respectively, during operation of the cell. For this pur-- pose, an anolyte circulation system comprising conduits for withdrawing anolyte from the anolyte compartment and for returning anolyte so withdrawn" to the anolyte compartment is provided. Suitable tanks and pumps are arranged in the anolyte circulation system for eiificient handling of the anoiyte. The lead borate produced during operation of the cell is separated returned thereto.

In operating the cell to produce lead borate, an electric current is passed from the anode through the anolyte, the diaphragm and the catholyte to the cathode. Satisfactory operation is secured with a potential difference of about 3 to 6 volts between the anode and the cathode, and a current density of about 15 amperes per square foot. The reactions occurring during electrolysis probably proceed substantially as follows:

The sodium chlorate in the anolyte reacts with the lead anode to form lead chlorate and to liberate sodium which migrates to the cathode where it combines with water to produce sodium hydroxide and liberate hydrogen:

Sodium tetraborate and sodium hydroxide from the catholyte diffuse through the diaphragm into the anolyte and react with the lead chlorate to precipitate lead borate and to regenerate the sodium chlorate:

The tendency for the alkalinity of the catholyte to increase owing to the migration of sodium ions and the production of sodium hydroxide at the cathode is compensated for by the addition of boric acid to the catholyte externally of the cell:

It will be observed that the only reagents actually consumed during operation 01' the cell are the lead of the anode and the boric acid which is added to the catholyte. Some water is also consumed, but in rather small amount. The sodium chlorate is wholly regenerated, and it is therefore necessary to add. only such amounts of this reagent as are unavoidably lost through spillage, leakage from the cells and conduits, and similar operating losses.

Insome cases it is advantageous to maintain the catholyte under a slightly greater hydrostatic head than the anolyte. In this way any tendency of the sodium chlorate to diiIuse through the diaphragm from the anolyte to the catholyte is diminished and at thesame time difiusion of sodium tetraborate and sodium hydroxide from the catholyte to the anolyte, which is desired in order to precipitate the lead borate and to regenerate the sodium chlorate, is aided.

The physical characteristics of the product of the cell may be varied considerably by variations in conditions prevailing in the cell during electrolysis. The following factors exert particular influence in this direction and should be properly controlled to secure a lead borate product having optimum physical qualities for the use to which it is to be put and to facilitate operation of the cell:

z-cotcentmtm of salts in the electrolyte Concentration of borate in the anolyte should be maintained at about 1.0% to 1.25% by weight Na2B4o7 in order not to interfere with corrosion of the anode; at the same time it is desirable to -maintain this concentration in order to control 2-Soluble lead It is important to avoid accumulating any considerable amount of soluble lead in the ano- Lyte, for otherwise the soluble lead will be occluded in the lead borate precipitate. Soluble lead in the precipitate renders the lead borate of questionable value as a material for the ceramic industry. The concentration of soluble lead in the anolyte may be controlled by properly regulating the alkalinity of the anolyte.

3-Alkalinity of anolyte The alkalinity of the anolyte should be maintained at avalue corresponding to a pH of between about 8.2 and about 92. Below this lower value soluble lead accumulates in the anolyte to such an extent as to seriously impair the value of the precipitated lead borate as a ceramic material. Above the upper value (pH 9.2), the lead borate is precipitated as an encrustation onthe anode and thereby introduces practical difflculties in carrying out the electrolytic operation.

We claim:

1. The method of producing lead borate which comprises passing an electric current through a cell comprising a lead anode. an anolyte comprising an aqueous solution of sodium chlorate, a diaphragm, a catholyte comprising an aqueous solution of sodium tetraborate, and an insoluble cathode. a

2. In an electrolytic process for the production of lead borate in a bifiuid cell comprising an anolyte containing a substance capable upon eleotrolysis of serving as a solvent for lead and a catholyte comprising an aqueous solution of a borate, the improvement which comprises employing as theanolyte an aqueous solution comprising an ionizable chlorate salt capable of serving upon electrolysis as a solvent for lead. 3. In an electrolytic process for the production of lead borate in a bifiuid cell comprising an anolyte containing a. substance capable upon electrolysis of serving as a. solvent for lead and a catholyte comprising an aqueous solution of a borate, the improvement which comprises employing as an anolyte an aqueous solution of sodium chlorate.

4. In an electrolytic process for the production of lead borate in a bifiuid cell comprising an anolyte containing a substance capable upon elecploying as a catholyte an aqueous solution of sodium tetraborate.

5. The method of producing lead borate which comprises passing an electric current through a 7 cell comprising a lead anode, an anolyte comprising an aqueous solution of sodium chlorate, a diaphragm, an insoluble cathode, and'a catholyte comprising an aqueous solution of sodium tetraborate, and maintaining in the anolyte so dium tetraborate in amount equal to about 1.0 percent to 1.25 percent by weight.

6. The method of producing lead borate which comprises passing an electric current through a cell comprising a lead anode, an anolyte comprising an aqueous solutionoi sodium chlorate, a diaphragm, an insoluble cathode, and a catholyte comprising an aqueous solution of sodium tetraborate, and maintaining the catholyte substantially saturated with respect to sodium tetraborate.

7. The method of producing lead borate which comprises passing an electric current through a cell comprising a lead anode, an anolyte comprising an aqueous solution of sodium chlorate, a diaphragm, an insoluble cathode, and a catholyte comprising an aqueous solution oi sodium tetraborate, and maintaining in the catholyte a concentration of sodium tetraboratev equal to 8. The method of producing lead borate which comprises passing an electric current through a cell comprising a lead anode, an anoiyte comprising an aqueous solution of sodium chlorate, a diaphragm, an insoluble cathode, and a catholyte comprising an aqueous solution \of sodium tetraborate, and maintaining the hydrogen ion concentration of the anolyte at a value equivalent to a pH of about 8.2 to 9.2.

9. The method of producing lead borate' which comprises passing an electric current through a cell comprising a lead anode, an anolyte comprising an aqueous solution of sodium chlorate, a diaphragm, an insoluble cathode, and a catholytecomprising an aqueous solution of sodium tetraborate, maintaining in the anolyte-sodium tetraborate in amount equal to about 1.0 percent to 1.25 percent by weight, maintaining the oath-- olyte substantially saturated with respect to sodium tetraborate, and maintaining the hydrogen ion concentration of the anolyte at a value equivalentto a pH of about 8.2 to 9.2.

STEPHEN W. STOCKDALE. ELBERT F. WEAVER. SAMUEL PI UL TINNES. 

